Understanding System Message Logging

By default, access points send the output from system messages and debug privileged EXEC commands to a logging process. The logging process controls the distribution of logging messages to various destinations, such as the logging buffer, terminal lines, or a UNIX syslog server, depending on your configuration. The process also sends messages to the console.

Note The syslog format is compatible with 4.3 BSD UNIX.

When the logging process is disabled, messages are sent only to the console. The messages are sent as they are generated, so message and debug output are interspersed with prompts or output from other commands. Messages are displayed on the console after the process that generated them has finished.

You can set the severity level of the messages to control the type of messages displayed on the console and each of the destinations. You can timestamp log messages or set the syslog source address to enhance real-time debugging and management.

You can access logged system messages by using the access point command-line interface (CLI) or by saving them to a properly configured syslog server. The access point software saves syslog messages in an internal buffer. You can remotely monitor system messages by accessing the access point through Telnet or by viewing the logs on a syslog server.

Configuring System Message Logging

This section describes how to configure system message logging. It contains this configuration information:

System Log Message Format

System log messages can contain up to 80 characters and a percent sign (%), which follows the optional sequence number or timestamp information, if configured. Messages are displayed in this format:

seq no:timestamp: %facility-severity-MNEMONIC:description

The part of the message preceding the percent sign depends on the setting of the service sequence-numbers, service timestamps log datetime, service timestamps log datetime [localtime] [msec] [show-timezone], or service timestamps log uptime global configuration command.

The facility to which the message refers (for example, SNMP, SYS, and so forth). A facility can be a hardware device, a protocol, or a module of the system software. It denotes the source or the cause of the system message.

severity

Single-digit code from 0 to 7 that is the severity of the message. For a description of the severity levels, see Table 21-3.

MNEMONIC

Text string that uniquely describes the message.

description

Text string containing detailed information about the event being reported.

This example shows a partial access point system message:

00:00:46: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up

00:00:47: %LINK-3-UPDOWN: Interface GigabitEthernet0/1, changed state to up

00:00:47: %LINK-3-UPDOWN: Interface GigabitEthernet0/2, changed state to up

00:00:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface Vlan1, changed state to down

00:00:48: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet0/1, changed
state to down 2

Disabling and Enabling Message Logging

Message logging is enabled by default. It must be enabled to send messages to any destination other than the console. When enabled, log messages are sent to a logging process, which logs messages to designated locations asynchronously to the processes that generated the messages.

Disabling the logging process can slow down the access point because a process must wait until the messages are written to the console before continuing. When the logging process is disabled, messages are displayed on the console as soon as they are produced, often appearing in the middle of command output.

To re-enable message logging after it has been disabled, use the logging on global configuration command.

Setting the Message Display Destination Device

If message logging is enabled, you can send messages to specific locations in addition to the console. Beginning in privileged EXEC mode, use one or more of the following commands to specify the locations that receive messages:

Note Do not make the buffer size too large because the access point could run out of memory for other tasks. Use the show memory privileged EXEC command to view the free processor memory on the access point; however, this value is the maximum available, and you should not set the buffer size to this amount.

Step 3

logging host

Log messages to a UNIX syslog server host.

For host, specify the name or IP address of the host to be used as the syslog server.

To build a list of syslog servers that receive logging messages, enter this command more than once.

Terminal parameter-setting commands are set locally and do not remain in effect after the session has ended. You must perform this step for each session to see the debugging messages.

Step 6

show running-config

Verify your entries.

Step 7

copy running-config startup-config

(Optional) Save your entries in the configuration file.

The logging buffered global configuration command copies logging messages to an internal buffer. The buffer is circular, so newer messages overwrite older messages after the buffer is full. To display the messages that are logged in the buffer, use the show logging privileged EXEC command. The first message displayed is the oldest message in the buffer. To clear the contents of the buffer, use the clear logging privileged EXEC command.

To disable logging to the console, use the no logging console global configuration command. To disable logging to a file, use the no logging file [severity-level-number |type] global configuration command.

The first command enables timestamps on log messages, showing the time since the system was rebooted.

The second command enables timestamps on log messages. Depending on the options selected, the timestamp can include the date, time in milliseconds relative to the local time zone, and the time zone name.

Step 3

end

Return to privileged EXEC mode.

Step 4

show running-config

Verify your entries.

Step 5

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To disable timestamps for both debug and log messages, use the no service timestamps global configuration command.

This example shows part of a logging display with the service timestamps log datetime global configuration command enabled:

This example shows part of a logging display with the service timestamps log uptime global configuration command enabled:

00:00:46: %LINK-3-UPDOWN: Interface Port-channel1, changed state to up

Enabling and Disabling Sequence Numbers in Log Messages

Because there is a chance that more than one log message can have the same timestamp, you can display messages with sequence numbers so that you can unambiguously refer to a single message. By default, sequence numbers in log messages are not displayed.

Note Specifying a level causes messages at that level and numerically lower levels to be displayed at the destination.

To disable logging to the console, use the no logging console global configuration command. To disable logging to a terminal other than the console, use the no logging monitor global configuration command. To disable logging to syslog servers, use the no logging trap global configuration command.

Table 21-3 describes the level keywords. It also lists the corresponding UNIX syslog definitions from the most severe level to the least severe level.

Table 21-3 Message Logging Level Keywords

Level Keyword

Level

Description

Syslog Definition

emergencies

0

System unstable

LOG_EMERG

alerts

1

Immediate action needed

LOG_ALERT

critical

2

Critical conditions

LOG_CRIT

errors

3

Error conditions

LOG_ERR

warnings

4

Warning conditions

LOG_WARNING

notifications

5

Normal but significant condition

LOG_NOTICE

informational

6

Informational messages only

LOG_INFO

debugging

7

Debugging messages

LOG_DEBUG

The software generates four other categories of messages:

•Error messages about software or hardware malfunctions, displayed at levels warnings through emergencies. These types of messages mean that the functionality of the access point is affected.

•Output from the debug commands, displayed at the debugging level. Debug commands are typically used only by the Technical Assistance Center (TAC).

•Interface up or down transitions and system restart messages, displayed at the notifications level. This message is only for information; access point functionality is not affected.

•Reload requests and low-process stack messages, displayed at the informational level. This message is only for information; access point functionality is not affected.

Limiting Syslog Messages Sent to the History Table and to SNMP

If you have enabled syslog message traps to be sent to an SNMP network management station by using the snmp-server enable trap global configuration command, you can change the level of messages sent and stored in the access point history table. You can also change the number of messages that are stored in the history table.

Messages are stored in the history table because SNMP traps are not guaranteed to reach their destination. By default, one message of the level warning and numerically lower levels (see Table 21-3) are stored in the history table even if syslog traps are not enabled.

Beginning in privileged EXEC mode, follow these steps to change the level and history table size defaults:

When the history table is full (it contains the maximum number of message entries specified with the logging history size global configuration command), the oldest message entry is deleted from the table to allow the new message entry to be stored.

To return the logging of syslog messages to the default level, use the no logging history global configuration command. To return the number of messages in the history table to the default value, use the no logging history size global configuration command.

Setting a Logging Rate Limit

You can enable a limit on the number of messages that the access point logs per second. You can enable the limit for all messages or for messages sent to the console, and you can specify that messages of a specific severity are exempt from the limit.

•(Optional) Apply the limit to all logging or only to messages logged to the console.

•(Optional) Exempt a specific severity from the limit.

Step 3

end

Return to privileged EXEC mode.

Step 4

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To disable the rate limit, use the no logging rate-limit global configuration command.

Configuring UNIX Syslog Servers

The next sections describe how to configure the 4.3 BSD UNIX server syslog daemon and define the UNIX system logging facility.

Logging Messages to a UNIX Syslog Daemon

Before you can send system log messages to a UNIX syslog server, you must configure the syslog daemon on a UNIX server. Log in as root, and perform these steps:

Note Some recent versions of UNIX syslog daemons no longer accept by default syslog packets from the network. If this is the case with your system, use the UNIX man syslogd command to determine what options must be added to or removed from the syslog command line to enable logging of remote syslog messages.

Step 1 Add a line such as the following to the file /etc/syslog.conf:

local7.debug /usr/adm/logs/cisco.log

The local7 keyword specifies the logging facility to be used; seeTable 21-4for information on the facilities. The debug keyword specifies the syslog level; see Table 21-3 for information on the severity levels. The syslog daemon sends messages at this level or at a more severe level to the file specified in the next field. The file must already exist, and the syslog daemon must have permission to write to it.

Step 2 Create the log file by entering these commands at the UNIX shell prompt:

$ touch /usr/adm/log/cisco.log

$ chmod 666 /usr/adm/log/cisco.log

Step 3 Make sure the syslog daemon reads the new changes by entering this command:

$ kill -HUP `cat /etc/syslog.pid`

For more information, see the man syslog.conf and man syslogd commands on your UNIX system.

Configuring the UNIX System Logging Facility

When sending system log messages to an external device, you can cause the access point to identify its messages as originating from any of the UNIX syslog facilities.

Configure the syslog facility. See Table 21-4 for facility-type keywords.

The default is local7.

Step 5

end

Return to privileged EXEC mode.

Step 6

show running-config

Verify your entries.

Step 7

copy running-config startup-config

(Optional) Save your entries in the configuration file.

To remove a syslog server, use the no logginghost global configuration command, and specify the syslog server IP address. To disable logging to syslog servers, enter the no logging trap global configuration command.

Table 21-4 lists the 4.3 BSD UNIX system facilities supported by the Cisco IOS software. For more information about these facilities, consult the operator's manual for your UNIX operating system.

Table 21-4 Logging Facility-Type Keywords

Facility Type Keyword

Description

auth

Authorization system

cron

Cron facility

daemon

System daemon

kern

Kernel

local0-7

Locally defined messages

lpr

Line printer system

mail

Mail system

news

USENET news

sys9

System use

sys10

System use

sys11

System use

sys12

System use

sys13

System use

sys14

System use

syslog

System log

user

User process

uucp

UNIX-to-UNIX copy system

Displaying the Logging Configuration

To display the current logging configuration and the contents of the log buffer, use the show logging privileged EXEC command. For information about the fields in this display, refer to the Cisco IOS Configuration Fundamentals Command Reference for Release 12.2.

To display the logging history file, use the show logging history privileged EXEC command.